Description
The Moon is Earth's only natural satellite and is the fifth-largest moon in our solar system. It is sometimes referred to by its Latin name, Luna. Most moons in the solar system are very small, but there are a few large, planet-like moons. Our Moon is one of them. Although there are moons in the solar system even larger than our Moon (namely Ganymede, Titan, Callisto, and Io), Earth and the Moon are sometimes referred to as double planets because the Moon is not very small compared to Earth: its mass is 1/81 that of Earth. However, the common center of mass around which Earth and Moon orbit is still inside Earth. Only in the case of the dwarf planet Pluto and its moon Charon is the moon proportionally larger, at 1/8 the planet's mass, and does the common center of mass lie outside Pluto. Because the Moon orbits Earth in an elliptical fashion, the distance between the Moon and Earth varies. The point where the Moon is farthest from Earth is called apogee (distance between the Moon and Earth: 405,500 km) and the point where the Moon is closest to Earth is called perigee (distance: 363,345 km). The average is 384,450 km. If a full moon occurs during perigee (such as on June 23, 2013), it is also called a supermoon. Over time, the distance between the Moon and Earth has steadily increased. Currently, the annual increase is four centimeters per year
